Trying to FIX a FLUKE 73 MULTIMETER which Measures 9V as 3000V
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- čas přidán 27. 08. 2024
- Hi, in this video I attempt to repair a Fluke 73 Multimeter sent in by a viewer named Lee. He purchased it at a car boot sale but it is giving strange readings. The fuses are fine so let's see it it can be fixed.
Remember that this is just for entertainment and I am not an expert in these repairs. The processes in the video may not be the best way, the correct way or the safest way to fix these things. I do love fault finding and trying to fix broken things, so I hope that comes across in this 'Trying to FIX' series. Many thanks, Vince.
Hi Vince, I sent the meter in ..... Love the fact you show the fail videos too, but on this occasion I wish the fault had been found ...... Really looking forward to a revisit ... Thanks for trying, great video.
Cheers Lee, I wish I could have fixed it but maybe we'll win on a revisit. I am reading though all the comments and hopefully a revisit video may sort it. Thanks again for sending it over :-)
@@Mymatevince Before it get's lost in all those comments about that resettable resistor... There's a huge crack in the yellow ceramic capacitor right above the fuses.
Edit: Turns out that is a spark gap.
@@Mobin92 Good Eyes that yellow ceramic capacitor does have a huge Crack in it by the looks of it
@@Mobin92 it's not a crack. It is a spark gap. That's how it should be. Karl
I used to be like Vince 15 years ago. If I could revisit myself 15 years ago, I still would not have been able to help myself fix these electronics. The whole problem is in understanding how these electronics were never meant to be repaired in the first place. So I gave up on this whole adventure after that. Good luck my mate Vince.
Try asking help from CZcamsr "Ben Heck Hacks".
Fluke meters are so reliable that I would think twice before putting my hands near that 3kv battery...
LOL =D
Haha, yes, don't test that bad boy with the tip of your tongue!
Haha :-)
Yeah they are very good most that were in at the calibration company I used to work for often just had fuses changed etc and went straight out with new certificates 🙂
My Fluke 75 I've had since the late eighties.
Vince don't let the haters put you down, as you said it's a 'trying to fix' video and i think most would agree that no matter what the end result is, it's still entertaining :)
Hey Vince. regarding the AC volts not working - This implies capacitor C1 being bad (or maybe a bad conection to it - looking at the video, there seems to be a lot of corrosion on the pins of C1. This is a 22nF (0.022uF), 1000V rated mylar film capacitor, but you could swap it for pretty much any 22nF cap just for testing purposes. Most likely the corrosion on the legs is the issue here as this part rarely fails on its own.
EDIT - I posted this before the end of the video, and it looks like you've tested the cap to be OK, so I'd give the mode selector switch a very close look as the only real difference between the ACV and DCV ranges is C1, so as the DCV range works (albeit inaccurately) and the ACV doesn't, then check the switch given that C1 is OK
The AC voltage is converted to DC by a precision rectifier inside U1 before being filtered, buffered and then fed to the analogue to digital converter.
As for the inaccurate voltage readings, it might be worth checking the ground end of the voltage divider Z1 (This is basically just a bunch of high-precision, high stability resistors on a single substrate). If the ground reference on Z1 is not good, it could cause all manner of incorrect measurements (generally causing the meter to read high - in much the same way that a bad ground on a volume control potentiometer will cause your amplifier to be blasting at full volume)
The ground end of Z1 is on pin 7 according to my schematic, and this goes to a pair of transistors (Q1 and Q2) which appear to be configured as a voltage reference or current source - it might be worth checking these too, as any issues here could cause wacky measurements, and these components have been known to fail in these meters, but it's highly improbable that Z1 itself will be faulty, but those transistors have been known to go short circuit, so you should be able to test them with your working meter or better still, with your component tester. Because of the way these are wired up, in-circuit testing may not be reliable so most likely you'll have to pull them out to test them properly.
Also, check the voltage at the junction of R15 and R16 - This should be 1V exactly - this is the reference voltage for the analogue-to-digital converter inside U1(If this voltage is wrong or missing, then check Q3 and the 1.2V zener diode VR1. If the voltage is present but not correct, it can be adjusted by the calibration pot R8. If adjusting R8 fails to get the voltage correct, then I'd suspect the zener and/or Q3. If the 1V reference is correct, then check that this voltage is also present at pin 14 of U1. If not, suspect a bad track on the board.
My service manual covers all the Fluke 7x-series meters but is quite old and appears to be hand-drawn, so it's not quite as easy to follow as a more modern diagram, and also includes a signal-flow diagram too in order to make it easier to follow what's going on, as well as board layouts for various models. If you're interested in this, I got the complete service manual from here;
bee.mif.pg.gda.pl/ciasteczkowypotwor/Fluke/FLUKE%2077,%2075,%2073,%2070,%2023,%2021%20Series%20II%20Service.pdf
This also includes a very comprehensive fault-finding chart and testing / calibration procedures.
(I hope that link works - CZcams REALLY hates me posting links in the comments)
If I had to guess, I'd suspect the Analogue Processor chip U1 (the Fluke-branded custom chip under the battery area - the other one is the display driver, and that seems to be working just fine), but I'd want to check all the other parts first. Generally speaking, Fluke meters (well the old ones anyway) tend be be quite reliable,
Good luck Vince!
That's really useful and I hope CZcams leave your link there as I reckon with all that info we COULD have a revisit soon.
Only thing I notice with the videos is the lack of a plan of action. Do we check for continuity, check components, desolder chips or just have a little think 🙂
Not complaining though as that's what makes these videos real and not like watching a repair shop. I never skip anything and just watch the full video.
Well done for your patience and perseverance 👍
@@bob3460 It's often tempting to dive right in and start checking everything we can think of, and I think we all do that, but after a while, you start to figure out what's going on and start closing in on the fault.
A lot depends on if you have the schematic available. If you do, then it doesn't hurt to spend a bit of time studying it to determine the signal path through the device. Once you have that sussed out, it becomes easier to devise a set of procedures to follow, but even then it's easy to miss the simple things so it's always a good plan to check eveything that comes to mind :)
I used to do electronics servicing for a living back in my youth - these days it's just a hobby, but I have to say that Vince has learned a huge amount in a short time - I wish I'd had CZcams when I was learning this stuff 40-odd years ago :)
Brilliant advice Count, thanks for taking the time to post it :-)
Vince , I have to thank you once more 😀, I have purchased a non working Google Home from eBay ( mic not working ) and I thought what would Vince do . So I used some compressed air on the mic. Now my son has a working Google Home. Thanks so much for being an inspiration to us all 😁
I always like it when I open up CZcams and see a MyMateVince video that's over an hour long. Thanks Vince!
Thanks Michael :-)
Have an identical meter but slightly different fault, reading wrong volts and ohms. Watched the video then took mine apart and saw some corrosion around the battery, so used some PCB cleaner and scraped the battery contacts, and it was still doing the same thing, but gradually started to work correctly. I think the cleaner took some time to dry off and now I have a working meter. Thanks for the video.
Glad I'm not the only one who knows how to use the multimeter but not a clue how to fix it if it breaks 🤣 great video as always bud 👍
If you can find a publicly available service manual for a product you know you have something that the manufacturer meant you to repair it and a great way to know if the device your getting is backed up by a consumer friendly company. A good service manual is a HUGE pro for any product you can buy. Its a welcome sight in our throw away seociety.
That should be a worldwide petition, and let's see how many ppl that would reach 😊
I am lucky my fluke never broke even after about 20 years later. Good info bro👍
yeh same here
It's very rare for them to go wrong even more so if they are calibrated once a year to keep them in tolerance.
Testing a Multi Meter with a Multi Meter that's may a bit weird but it works great. I like that you gave it an attempt and I am really hoping for a revisit video on that.
Fantastic video. I haven't been watching CZcams in a while, it's amazing to see how far you've progressed with your technical troubleshooting abilities. Top notch professional now.
Looks like the possible fault list you have jives with the schematic. The fact that AC is bad also means that S1 is not the problem as AC measurement doesn't go through S1. In AC mode the signal goes from J1 through R1 through C1 then into Z1 pin 1 and out pin 2, then straight to U1 pin 31. In DC mode the signal goes though R1 then into S1 pin 2 and out S1 pin 1 bypassing C1, then to Z1 pin 1 out pin 2, then straight to U1 pin 31.
Possible faults are then R1 out of tolerance (should be 1K ohm), or Z1 (resistor divider) between pins 1 and 2 out of tolerance (should be 1M ohm) or U1 is bad. If the voltage at U1 pin 8 is near 9 volts, I would suspect U1 is not measuring the battery voltage correctly either. Thus, giving you the low battery signal. If that is the case then it also points to U1 as the culprit.
The allowable tolerance of R1 can be read off of the color bands (Google resistor color codes) Given the age of the meter it will most likely be a four band code. the last (fourth) band (gold 5% or silver 10% or no band 20%) will be the tolerance. If the fourth band is any other color it has an even tighter tolerance. Check the color chart. I don't have them all memorized :(
Lift one leg to measure the resistor out of circuit (one leg of the resistor, not your leg).
I want him to lift his legs and then take measure of those resistors😂😂😂
Let's see how that works
It's not a simple tolerance problem. Did you notice the voltage stays at 3000 v (well floating around) after he stops touching the battery? If it were in the divider it would still drop back to zero correctly.
Hahahah. "One leg of the resistor, not your leg", i cackled. :)
Haha :-)
Thanks for the fault finding tips Jeffrey :-)
@@GigsVT I've seen this too but i have no idea what could lead to this behaviour.
I enjoyed the video using a multimeter to fix a multimeter can’t wait to see the revisit
According to the schematic, the resettable resistor should be a a 1.2k ohm and the readings you where reading was in the high ‘k’ ohms. Worth a double check.
It was a great attempt, I always love it when you go into the details of how these things work. Keep up the amazing work with the Trying To Fix videos! 👍
This is why i love your channel ......not knowing whether your going to fix it or not is very entertaining and enjoyable ....in my opinion if I already new what the outcome of the fix was going to be it wouldn't be as interesting......so failing to fix something is just as enjoyable and entertaining as when you fix something... this is my opinion anyway.....Thankyou for all these videos you upload I look forward to them all.... :)
Cheers Colin :-)
Hey Vince, check the resettable resistor. Ive got a fluke 23 which had similar problems when I accidentally hooked up to a variable speed drive.i replaced that resistor and it worked, please check it out of circuit. Hope this works👍
My money is on that crystal. The low battery assumption, can also be due to wrong clock.
@@kruleworld Yes, vince calls it resettable, but the schematic doesn't, and I doubt they are. The fusible part means that the resistor will burn to an open, protecting the remaining circuitry. Check these resistors out of circuit, the colour code will be what you should read. Also check the fuses with an actual ohm setting. Just because the meter "beeps" doesn't mean the fuse is reading zero like it should. I recently ran into a situation where a system powered up with little load, but when you placed a load on it, the voltage dropped significantly. The fuse showed 300 ohms when measured! Crazy. Just something else to rule out.
I had a broken one before... Got it to read right once, but that was just a Fluke .
Always enjoy watching your videos. Shame it's not fixed yet. Reading the comments that someone replaced R1 with a 1M ohm instead of 1K ohm resistor would certainly be a good thing to check. That's 1000x too high. Also measuring that voltage divider for resistance between pins is also worthwhile. Looks like your fans have come up with good suggestions. Losing 0.1v when in circuit also seems a bit excessive. Look forward to the revisit. You might fix this yet.
I once had a Megger tester, it was a MFT tester for electrical installations, and that was giving me all sorts of funny readings, when I pulled the thing apart, there was a lot of carbon build up inside the switch, after cleaning that selector switch it worked perfectly, could be the same issue, also there is normally an adjustment screw which is used when they go for calibration and they use to adjust if the meter is out.
Learned a lot just from your technic. thanks
Hard luck mate. Have a Fluke Multimeter myself so enjoyed seeing what makes them tick. Keep up the good work. Mick 😁🍻
Hi Vince. This age of meter uses a fusible resistor. You really need to desolder that one in the input circuit and check it. Also, to sort the ohms reading out there is an adjustable pot you can tweak so you could maybe make it usable just for that if the voltage range cannot be sorted. Another thought is corrosion on the vias from top to bottom of the board? Love your vids and your patience. Cheers.
My multimeter had similar issues after lying in a damp garage with a leaking battery for some time. With my oscilloscope I could see that the oscillator was not running. Heating the ceramic capacitors (33p and 47p) with a heatgun would wake up the multimeter, but with unstable ohm readings. Coldspray would stop the oscillator again. After replacing all ceramic capacitors (there is another 33p and a 220n) it worked ok again.
just looked at the online manual - there should be precisely 1v at the junction of R15 and R16 and can be adjusted via R8 - but be careful you may ruin its calibration {though looks to me its a bit late to worry about that lol] If you do indeed have precisely 1volt then the chip under the battery [U1] is shot - have now got the manual - if you want it, give me a clue as to how i can send it you {its over 5.5meg} keep up the good work
Andy
I skipped through to the end - guessed it was no go but fair play to you!
At 100:10 time mark when you where soldering the chip back on it looks like there is a small crack running through the top of the k down through the middle of the E
I see it too. Usually what I think is a crack on a chip is actually just a flux stain, but that definitely looks like it could be a blow hole.
Good eyes....I didn't notice that, you could be right, could be flux though...worth an investigation 👍
very nice spot. That does indeed look like a crack and not flux Guess a new chip is needed
Here’s a screenshot. There’s definitely something there... pasteboard.co/JnVGpoS.jpg
Ohhhh that's disappointing. I would like a revisit video on this but maybe I should check out this crack first..... I am hoping it is a hair!!!!
I have one of these 73III meters and I had the mad readings like that one ..it was the rotary selector switch in my case , In my case though it was very obvious some thing corrosive had spilt onto the switch area in when it was in the bottom of my tool bag as the dial was discoloured..I got a second hand unit with a broken case and made one good out of the two...I still only use it as a back up to my trusty fluke 177...sometimes you need to measure two voltages at once , every sparkie needs more than one meter.
I'm happy I'm stil awake cuz it's 12:57 and I was wanting to watch a My Mate Vince video! Good job Vince :)
I always watch them late at night and end up falling asleep and have to finish in the morning.
I like your fault finding tools, in particular the osciloscope, good idea on using your power supply with the 9v also, I was routing for you but i did watch the video in 2 sittings!
I'm a new subscriber and I was watching another of your videos and thinking to myself, 'it would be cool to see him fix a multimeter,' only to have this immediately pop up in my recommended videos. Get out of my head CZcams!!
Love your videos Vince, great enthusiasm and tenacity......
That crystal looks like a clock crystal like the type you see in a watch...it is probably 32.768Khz, you measured 33Khz, close enough...
If you can get information on the supply voltage that should be present on the chips Vdd pins, check them, they may well be under voltage....
I suspect a reference voltage has gone out of spec for now.
Edit.....just made the above comment seconds before the schematic was shown....looks like that frequency was 32.768Khz.
E1 is a spark gap that will take >1500V to ground for safety.
As you zoom out, i saw that there should be Battery voltage on pin 8 of U1, also 0V on pin 40 of U1...(Check this to ensure there isn't a ground fault.)
Point to note...measuring across resistors in or out of circuit, the reading can't be ABOVE the depicted resistance + tolerance because you will always have a resistance across it via the circuit which will lower the reading. so that fusable 1K2 resistor shouldn't ever read more than 1K2+tolerance.
Looks like pin 18 of U2 should also have the same voltage as pin 8 of U1..check 21, 20 and 8 of U2 to for same voltage.
Video is slightly blured but make sure all ground pins are reading 0V on both chips, floating grounds could easily produce these symptoms....
Just seen a potential problem with a reference voltage and that is VM (Pin 20 of U2)...(Vdd / (R12+R11)) * R11, if the measured V at Vdd is 8V then VM should be 4.19V (Assuming input resistance of VM is very high.
Another reference Voltage would be VR1, looks like 1.22V, could be bad....
Pin 14 of U1 should be exactly 1.000V from VR1 reference and Q3 constant current source.
DON'T touch R8 yet, a calibration pot, can't think why this would be wrong unless someone has moved it...
Good luck Vince, hope you manage it and look forward to seeing your success
Thanks for the help Michael :-)
My immediate thought is the rotary switch. It looks like there's two separate layers, one controls what mode the main chip is in, the other re-routes analog signals in various ways. If the analog side has something up with it, then the chip could be getting voltages that are completely wrong for the mode it's in, so it displays nonsense? To me, the "3000 volts" result looks a lot like it thinks it's actually measuring a resistance. The fact it shows OL normally or when you measure the battery the other way round supports this idea, as a multimeter would typically do something like that if you try to measure a voltage while in resistance mode.
Edit: have seen that you tried cleaning and fiddling with the switch, it could still be something in that part of the circuit, even a bad solder joint if it's been dropped.
That’s exactly what i was thinking. O.L. Is only shown in resistance mode
I'm fairly new to this topic myself, but I think for you correctly testing the resistor, you have to solder one lead off, because it might have a path through the PCB somewhere that is giving it a lower resistance. (Or the resistor is in parallel with something somewhere.
Massive crack in that capacitor. Also, maybe the calibration pot is mucky.
I don't think it's a capacitor, it's a spark-gap device. Part of the protection circuitry.
that is not a capacitor its a spark gap & that calibration pot is just for the 3volt reference
Mate , I don`t care what others think , I feel you do a great job with your trying to fix videos because 1 you don`t know whats wrong 2 most of the time it`s something you`ve never seen 3 (sorry for this one ) you don`t know what you`re doing but you keep going in spite of it all , so sometimes you fail but it`s worth the adventure we both learn something
Personally I think you include the fails so I don`t feel like a failure when my repairs go wrong .
my guess is the previous owner had it apart and zapped it with static electricity , I killed my first digital multimeter that way by accident gotta watch out for that taught me to always use a ground strap even to change batteries
The rage at the end of the video i felt that we've all been there where we've spent hours doing something and it doesn't turn out how it should turn out i haven't seen the revisit video yet but hopefully you got it fixed and working.
For me the big clue is that the reading sticks at ~3000 for a little while after you disconnect the battery. That means that the input node of the ADC in the main chip has no good path to ground. It is supposed to go to ground through one of the resistors in the voltage divider hybrid: each resistor except the first 10M has its own pin into the ASIC, whch is presumably connected through a cmos switch to the ADC input where it meets the 10M to become the ground leg of the voltage divider.
Maybe the common connection of all the resistors in the hybrid isn't continuous to the hybrid's ground pin, so I think I'd remove the hybrid, and test from the common pin to each range-defining resistor. It looked like you did that in-circuit but it was hard to tell. IF the hybrid is ok and the hybrid's common pin is connected through the pcb to ground, then I'd wager the problem is in the ASIC. What are the oddds you could find an inexpensive donor meter with say the digital asic or the display bad but a good analog asic?
Thanks for the info Eric :-)
Things I would try - Try removing the voltage divider and see if the battery level indicator goes away (I would assume it would at least power on, but wouldnt measure stuff then). If the battery level indicator is unaffected by that, you could probably rule it out. My gut feeling is something has failed internally in the IC you focussed on. I would also remove the resistors on there and measure off the PCB, to be sure they are the correct size. That one that measures 0.6M seemed crazy to me tbh! Any diodes or transistors on there I would remove and measure off the PCB too.
Thanks for the tips Chris, I am hoping for a revisit on this one as lots of comments have come in :-)
Used to see quite a few fluke multimeters when I worked for a calibration company they used to go into the computer lab room.
I only used to get told when they were repaired or needed to go back to fluke if they were good they'd get a new calibration certificate and sent out 🙂.
The voltage divider is in the schematic you've found Vince, the remaining pins are on the bottom of the chip under "integrator/buffer" in the dashed box "z1". Simply remove the module from the board and you can measure if all the resistances check out as per the schematic.
I'd focus my efforts on the components in the "AC converter" and "Active filter" part (last page of schematic), both of which seems to be unused for resistance measurement (which works)...
Using scope, go after VDD on the "Analog processor" (battery input) - make sure it is at the full 9V when the unit is on. If not, start disconnecting stuff from VDD (the reference voltage 1.0V must be checked too - it is fed from VDD) If you disconnect stuff from VDD and suddenly the battery shows full, you onto it. Otherwise the internals of the chip may be fried. Meters die when they are overloaded mostly, although I have seen simple component level failures. My $20 ebay Fluke 27 series was just a bad test lead - very disappointing. You'll get it Vince!
Thanks for the tips David :-)
This meter shows 'OL' in VDC mode, while it should dance around 0V with open leads. So... what does it do when you short the leads while in VDC mode? I think that there's a voltage for some reason. You should measure that voltage on the test leads with your good multimeter. It should read 0V but as said, I suspect that there will be some voltage that shouldn't be there. So, if there's a voltage, please try to find out where it comes from.
You did not inspect the back side of that rotary mode selector switch, AFAIK. There's the on/off switch and there's a digital pushbutton. So, possibly, there's a blob of goo that leaks supply voltage or button voltage into the measuring circuit: VDC is consistently too high (OL) and your resistor measurements seemed to indicate on the low side for all resistors. You did not verify those resistors with your good multimeter. You also didn't short the leads. So, hard to say.
This voltage leak would explain the lit battery state indicator and the fact that it seems to use too much power (your Fluke supply battery voltage drops too much when the meter is on). But... how good is that supply battery, really? The Fluke might use an elaborate way to test its supply battery, for example by measuring its internal resistance, instead of the output voltage. That would be more accurate. I've seen 9V alkaline batteries that still put out 9V unloaded but when you try to use them to actually power something they turn out too weak.
Please do a follow-up. Please show us what the Fluke does in all modes with open leads, shorted leads and when doing an actual measurement. Just do not connect a known faulty meter like this directly to 240VAC mains power. Better use a transformer or just skip the VAC test.
And, of course, show us the back side of that switch and what's on the board under the switch. I'm very curious.
More suspenseful than the last 3 thrillers that I watched on Netflix. I think that your suspicion that the "battery did it" is still a valid deduction.
You absolutely must lift one end of a resistor to test it, especially if you suspect it's open cct, as any readings could be from elsewhere in the circuit. The two identical resistors look like 1Mohm brown black green. Another thought is that the battery voltage appears to drop to below 9v when the meter is on, that suggests that the meter is pulling more current then it should, also I suspect the reason for the low batt symbol. Maybe try powering the meter from your bench PSU instead of the batt and see how much current it takes. If it is using too much current see if anything gets warm to the touch. Also see if the batt symbol disappears. Love your videos 👍
Thanks Adam :-)
it seem there is a crack on fluke chip 1:00:13 between "KE"
Ah yes! that might be nothing, or that could be it!!
And chip
Hya Vince. Another fab video (as always) I'll take that multimeter off your hands if you don't need it anymore!
Great video vince I found it interesting
Hi Vince, there should be a pair of transistors on the input. They are really fast and are used for input protection. If they blow strange things happen. This is a common fault for this type of equipment. They will start conducting an together with a VDR and other stuff are part of the input protection circuit. However, I need to note that if they are blown the Fluke had some serious stuff going on. Hope you will fix it.
Thanks Johan :-)
Love this man
I know I'm late to the party on this video. It's 2 yrs old attire of this post. Whenever I see battery leak I check all the traces under my microscope. You would be surprised how much time I wasted on a trace that has a hairline break. Now it's the first think I look for before even looking at components.
The thick black resistor next to the 1Mohm is a wirewound precision resistor with 1% tolerance, value will probably be written on the body. I suspect the re-settable device is the green disc shaped component below the two resistors.
I hope you have fixed this by now. It is the fusible resistor 1k that is faulty
just above the fuses isnt that component cracked in the middle? the orange brown cap looking thng? above the 2 red components?
spark gap
@@SloVu thanks just a thought.
The battery symbol is on upper left corner is on , so the 9 volt battery in it is low or it is reading as low battery .when you have a low battery in it will not read actuate.
That was an excellent try, Vince. I do not think that it is repairable, you would need parts that are not available. Again , good try.👍👍
Test equipment sold in car boot sales are usually damaged or more likely stolen ,no one throws away an expensive test meter!
Great video. I hope you can make a revisit.
Hi Vince The first thing you should have done is lift the one side of that resistor and check it out of circuit, as the value didn't match the colour coding,
Check R1, you should have an 1Kohm resistor, when you measure on circuit you get almost 500Kohm, I believe that resistor is open, measure it off the circuit.
PS: I'm still seeing the video, don't know if you get it.
It's 1M Ohm - brown-black-green-gold, learn the colour code
And somebody is measure v to amp side and change fuse
@@technixbul or maybe red black green, it;s amazing how long Vince has been doing this and he still can't identify components, read resistor values, tell a capacitor from a rely, etc. UGH If it should be 1K somebody might have "fixed it already.
service manual dam-assets.fluke.com/s3fs-public/77______smeng0100.pdf
@@technixbul on the schematic it's 1K ohm, on the part list is 1K ohm, didn't look to the colors only to the measurements and schematic.
www.opweb.de/english/company/Fluke/73
Long time ago, on my job I had to know the colour code, but right now on the type of job I'm doing the resistors don't have colors. they are too small
Stick a post in the EEVBlog repair section Vince, some very clever guys on there. That was a great video btw and it was a big challenge.
The category markings you see on the multi-meter are industry standards as to what voltage level it will protect up to in rated catagory (in this case it is 600 Volts) and Category I is usually for light electronics, Category II is for anything up to your sockets including the sockets themselves, Category III is usually recommended from your sockets to your fuse-board, and Category IV is for the outside power lines themselves. Always make sure whenever dealing with household electricity get your hands on at least a Category II. I have seen some multi-meters that are Category III up to 500 Volts and then rated Category II up to a 1000 Volts.
Thanks Sarah :-)
Tks for The vídeo, 🎩
Well done Vince, nice fix ; ) Another testament to fluke I guess. Surprising though how puny those traces around a possible corrosive battery area are. Probably why they don't really enclose them with pcb's anymore. Battery compartments are the norm for the most part nowadays. Although with Li-on they seem to of back tracked to no compartments, tech huh.
Using a multimeter to fix a multimeter nice good. 👍
The yellow-orangeish component (most likely a capacitor?) just above the fuses seems to be badly cracked, gotta admit it was really frustrating to see a 1hr video without this being noticed... xD
i seen it too lol
@Senor Bob yeah thanks man, didn't know they make them like that - nice to learn new things.
MOVs(Metal Oxide Varistors) are for over-voltage protection.
Thank you, hope for a revisit!
The first check you did with the meter set on DC volts looks like it is set to measure resistance going by the display. DC volts on a Fluke doesn’t start with the display showing OL. Your fault may be with the selector switch.
I'm thinking the same thing. My father had a water damaged 73, some soldering of the battery contacts and some Deoxit and IPA on the selector fixed it.
I know what the problem is...... It's a proper flucked Fluke! 🤣
If you put it on DC volts, does it measure resistance?
Hi M8 the service manual sujests a way of testing meter and probabull causes of faults. Just google the meter and a manual will be available that covers several meters.
Thank you Vince
Sometimes you can't read the leads... My fluke (different model ) also goes crazy on really low batt. If you have battery sign, probably battery that feeds the ICs are not ok. Check regulators transistors etc, voltage of IC
Am I looking at the wrong schematic or is everyone missing the external voltage reference to the main chip?
Check the pin the voltage reference connects to, on the schematic I'm looking at it's labeled with the correct voltage. There's also a calibration adjustment pot there (maybe different on series III)
Looking at the insides of a Fluke 75 and 77, and there are notable differences in those resistors, etc. I wouldn't rely too heavily on the diagram you are using.
Search for the datasheet of the voltage devider it will give you the values of the resistors inside make a voltage devider out of resistors and solder it in the multimeter
10:11 At the moment. 1. Those fuses are just for Current measurment (the 2 last options. You say, you haven't tested yet) you can leave them off and the DVOM works still fine, as long as.. :D
...You don't try to measure a current. As then you have open loop inside DVOM that the meter don't show you.
2. As Battery on this model is there (most these days are outside so you don't assemble it wrong) and the fact that when the meter is open you can turn that selecting wheel 180 degree...
So maybe someone looked inside when they see the battery icon. Pull the battery out to go shop and meanwhile some one else find it and turns things around like some kind stress release toy.
3. if that isn't it. Then i would measure how far that 9 volts gets inside on different setting and whats common as it has to set that icon on all settings that isn't the "OFF"
Anyway i like your Trying to Fix it videos. Specially as mostly they arent all the same products like you sayed in begining.
Sorry my English have great day!
PS. That 1000V 11A fuse cost ~20€ today. So don't do "voltage measure" with ANY lead on A port, as then you burn literally money, with this DVOM.
I have Flukes and other DVOM's in dayly use and thats firsth that i See OL (Open Loop) reading on VDC setting when leads are not connected.
So still my "bet" is that wheel is 180degrees of and so it's sending voltage in wrong parts of the board and so messing up the screen reading.
44:25 Look your hand on black ground lead. Never touch the metal parts of the leads or the part you are takeing measure!
..as you are the one that is give it a different path to the multimetter, when you do so and so the measure isnt what it should be.
Sounds like a faulty fluke chip. But could be wrong. Hope you can get it to work.
Discrete parts looked okay, I suscept U2 and U2 may be a part of ADC.
Seems a bit strange that the readings started to get better after reflowing that chip the first time, do you think it was the heat on the chip made a difference until it cooled down again?
I’m guessing voltage divider. I’m guessing it steps down any incoming voltage to allow the chip to handle it. If it’s not working it’s reading something stupid on the chip because it’s not stepping down the voltage for the calculation. Also could explain the battery reading as almost dead? Probably easy to test the resistance though?
I have my fluke for 25 years still using it everyday
I like this new CZcams update
I hate it looks terrible
Yea it’s ugly af
I don’t like either
TheWizard22UK who uses Facebook
Sway on Kongzhi y your pfp move
When you read the diode under the LCD (time 39m47s) the meter read the right voltage 2.5v the is what most meters voltage out is to check diodes. Look from there.
Thank you Ripley
I'm surprised Vince that you didn't pick up on that. That says to me that the chip is fine. (Now voltage and resistance look ok) He basically bypassed the input components and got a good reading. I'd check out those to-92 package transistors with them out of circuit on the circuit tester. They are pretty low current devices and easily go down. Probably by design!
@@anthonydenn4345 it was quite an easy thing to miss but I agree with you the chip is probably fine
@@ripleysmith7583 Right Ripley ; ), nice to be proving correct. Funny how only yourself and meself picked up on something so telling! Vince just upped a fix vid. Turned out to be so much easier than what it first appeared. Love an easy fix : )
You can test it. Breath of the humidity breathing air to measurement cable hole and the reading will start to look crazy. Then solder all connections the rotary switch and carbon composition resistor
All this restoration and repair is driving hopes for people on eBay any more - no more junk repair finds
the resistors have a colour code and you can read them and tell what they are
I think that hybrid voltage divider is bad (especially the "ground" pin), Would be easy to desolder and ohm it out.
First thing that came to my mind was bad contact or short circuit under the selector contact wheel. Are you able to remove that and clean the contact points?
You might look into the A/D converter or the display driver outputs. I wonder if the issue is in the digital section (such as a bad A/D converter output, a bad display driver, etc). I would research which pins the digital signal comes out of the A/D and see if that is correct. Not sure if that is binary or BCD. If that is reading right, the problem is likely in the display driver. If not, likely the problem is in the A/D circuit. I am suspecting U1 is the A/D and the other big chip is the display driver but I could be wrong. I would also check the traces between the U1 and the other big chip, and possibly reflow that chip. It is possible that voltage and amperage use different pins as inputs to the chip, or possibly a mode select. I am not sure if there is another pin for the battery low indicator. You might start tracing or checking pins in this area.
Very lovely video vince
I don't know if you have just the schematic or the whole document but here is what it says to do...(amongst other stuff)...
Check the reference voltage.
You should get 1V at pin 14 of U1, or the junction of R15 and R16.
Also check the following...
Tracing the VDC signal path:
01. Set the unit to VDC and apply 2V dc across the probes.
02. Use your DMM and measure the voltage @ J1. It should be 2V.
03. Measure pin 1 of Z1 input divider. It should also be 2V.
If you don't get those voltages then R1, S1, RV1 or RV2 could be at fault.
(The following may be affected by loading)
04. Measure pin 3 of Z1. It should be 200mV. If not, Z1 or U1 could be at fault.
05. Measure the Active Filter Input (AFI, pin 26 of U1 or R9). It should also be 200mV. If not, U1 is at fault.
06. Measure the Active Filter Output (AFO, pin 27 of U1 or R9). It too should be 200mV. If not, R9, C5 or C6 could be at fault.
All these points are clearly marked on the schematic you show.
If all this checks out then at least it narrows it down a little further.
Also, the other 3 pins (8,9 and 10) for the resistor divider can be found at the bottom right of U1 in the schematic.
Thanks Mr Tom :-)
Take out R1 and check it. The colour bands appear to be brown black yellow from what I can make out which is 100KΩ. However the circuit diagram shows a 1KΩ resistor which is Brown black red. But either way when you measured you got a reading of 630KΩ. Which would mean that the resistor is open circuit and the 630KΩ is the resistance through the rest of the circuit.
As a test and not to be used without getting a proper part other than testing the 9v battery. I would suggest you put a 1KΩ resistor in place of R1 to see whether it gives a more accurate reading. As technixbul says below in the replies to this comment it looks like a 1MΩ resistor and according to the schematic diagram it should be 1KΩ. This would account for it being way out and would suggest that someone has already tried to repair the meter and put the wrong value in. The proper part according to the schematic diagram is a 1KΩ 2W fusible resistor.
If you test a resistor in circuit it can be lower than expected, but NEVER higher. Because in circuit the only thing that can affect the reading is if there is another resistive component in parallel, and resistors in parallel will ALWAYS lower the resistance. So @pds8475 is right, you should try and replace that resistor because its not right. Also, you can check the circuit diagram to see if the resistor have anything in parallel with it just to make sure
it was brown black green = 1M ... where you see yellow?
@@technixbul You may be right. I zoomed in on a section off the video last night and it appeared yellow but this morning when I zoom in on another part of the video it does look green. However the schematic diagram which covers the 73, 75 and 77 models show R1 as a 1KΩ 2W resistor. It does show some components are different between the models but lists the differences. The fusible resistors R1 and R20 however are not amongst them.
Also Z1 can be tested with resistance test. According to the schematic diagram there should be:
10MΩ between pins 1 and 2.
1.111MΩ between pins 7 and 3.
101.01KΩ between pins 7 and 4.
10.01KΩ between pins 7 and 5.
1KΩ between pins 7 and 6.
obviously those values will be tested on an accurate and calibrated meter but if yours shows similar results then I would suggest that Z1 is fine. Also remember that your meter has a limit to what it can read so pins 1 and 2 may be shown as 10MΩ or OL depending on your meter.
also R5 on the 73 model should be 390KΩ
Thanks for all the help on this :-)
Recently saw Adam Savage do a Video on Fluke Meters he recommended them.
I think the screen should show 0 volts and not OL in the voltage setting which is indicating you are not in the voltage measurement mode. Fuses are for current measurement protection.
It´s not fixed! NOOOOOOOOOO! ;-) Thanks for the great content!
Hello Vince, Thanks for the video. I have a Fluke 73 II Multimeter that is not working at all. The display has a few issues, (not clean) leaves some ghost images. Question is would it be worth repairing? The unit is in mint condition , even looking at the inside no rust, or corrosion. Any thoughts would be appreciated.
Your videos are awesome! I'm one of the U.S. versions of you (or aspire to be not with videos, just ability) but REALLY need to work on my patience. Your videos help me with that!
Please keep trying and if you DO figure this thing out, a revisit would be awesome =)